The long-term objective of the proposed research is to improve our understanding of how the binaural system facilitates the detection and recognition of complex sounds (i.e, sounds that have a bandwidth) in the presence of masking sounds. To date, few studies have provided an in depth investigation of binaural unmasking of complex signals and none has modeled the relevant results. The proposal has three specific goals: 1) to improve our understanding of how complex binaural objects are formed and localized, particularly when multiple images are detected, 2) to determine the degree to which the unmasking of a complex signal is dependent on the perceived spatial separation of the signal and masker, and 3) to develop, improve, and evaluate binaural- based models of unmasking capable of predicting the benefits to complex-signal detection. Two experimental paradigms are used. First, a complex signal (narrowband noise, or a multi-tone complex) is alternated with an acoustic pointer which the observer adjusts to match the perceived spatial position of the signal. In the second experimental paradigm, the degree to which spatial position affects unmasking is examined. Here, a complex sound (either a narrowband of noise, an AM or FM carrier, a two-tone complex, or a sequence of tone bursts defined by the pattern of intertone times) is presented in a background of a complex masker. The subject is required to indicate in which of two observation intervals the signal was presented. Both energetic and informational masking will be examined. The magnitude of binaural unmasking is usually very large, as great as 30 dB for narrowband maskers, and therefore has strong influences on auditory perception in natural environments. The results of the current experiments are expected to have further benefits for multi-channel hearing-aid design, and for basic theory and models of binaural interaction.